Control valves are commonly used in process control systems to control the flow of process fluids (e.g., liquids or gases). A control valve typically includes an actuator apparatus (e.g., a pneumatic actuator, a hydraulic actuator, etc.) operatively coupled to the flow control member of a fluid valve to automate the control valve. In operation, a controller is often employed to supply a control fluid (e.g., air) to the actuator which, in turn, positions the flow control member (e.g., a valve gate, a plug, a closure member, etc.) to a desired position relative to a valve seat to control or regulate the fluid flow through the valve.
As shown in FIG. 1, some known control valve assemblies 100 use a single spring actuator apparatus 110, which typically have an actuator 112, a yoke 140 that is used to couple the actuator apparatus 110 to the fluid valve 170, and a controller 160. Actuator 112 has an upper casing 116, having a vent assembly 118, and a lower casing 120 secured to upper casing 116 with nuts 122 and bolts 124 and defining a cavity 114. A diaphragm 130 is secured at its edge between upper casing 116 and lower casing 120 and at an inner portion between an upper diaphragm plate 136 and a lower diaphragm plate 138. Diaphragm 130 is positioned in cavity 114 to define an upper chamber 132 and a lower chamber 134. The examples discussed herein are directed to diaphragm actuators, however, the control valve assemblies could also contain piston actuators or any other well-known type of actuator.
Yoke 140 has a body 142 that is secured to actuator 112 at a first end of body 142 and to fluid valve 170 at a second end of body 142, opposite the first end. A generally L-shaped passageway 145 is formed in body 142 near the first end and is in fluid communication with an aperture 121 in lower casing 120 of actuator 112 to provide a control fluid (e.g., pneumatic air) from external tubing 162 to lower chamber 134 of actuator 112. An actuator stem 146 extends through body 142 and has a spring seat 148 positioned near one end and is operatively connected to diaphragm 130, through upper diaphragm plate 136 and lower diaphragm plate 138, via a cap screw 164. An actuator spring 150 is positioned within a cylindrical portion 144 of body 142 and extends between the first end of body 142 and spring seat 148 to bias actuator stem 146 away from actuator 112 and toward fluid valve 170. A spring adjuster 149 is threaded onto an end of actuator stem 146 and can be used to set the pre-load of actuator spring 150. A travel indicator 152 is mounted to body 142, near an end of actuator stem 146, and can be used to visually determine the position of flow control member 178 in fluid valve 170.
Controller 160 provides a control fluid (e.g., pneumatic air) to lower chamber 134 via external tubing 162 and passageway 145 in yoke 140 and can be mounted to yoke 140 or can be positioned in another location proximate actuator 112. Regardless of the mounting or positioning of controller 160, external tubing 162 is used to fluidly couple controller 160 and lower pressure chamber 134 of actuator 112. However, external tubing 162 can become damaged or dislodged, thereby affecting the accuracy of actuator apparatus 110 and, thus, a desired fluid flow through fluid valve 170.
Fluid valve 170 generally has a housing 172 that defines a fluid flow path from an inlet 174 to an outlet 176. A valve seat 180 is disposed with the fluid flow path and a flow control member 178 can be moved into and out of sealing contact with valve seat 180 to control the flow of fluid through fluid valve 170. A valve stem 182 extends from flow control member 178, through housing 172, and connects to actuator stem 146 via stem connector assembly 154.
In operation, controller 160 provides a control fluid through external tubing 162 and passageway 145 in yoke 140 to lower chamber 134 of actuator 112 to provide a pressure differential across diaphragm 130. The pressure differential causes diaphragm 130 to move actuator stem 146, and thus valve stem 182, such that flow control member 178 moves in a rectilinear path relative to valve seat 180 to control fluid flow through fluid valve 170.
However, external tubing 162 can become damaged or dislodged, thereby restricting or preventing the control fluid from flowing between controller 160 and lower chamber 134. For example, a process fluid flowing through fluid valve 170 may impart a frequency to control valve assembly 100 that is substantially equal to a resonant frequency of actuator 112 and/or control valve assembly 100, causing actuator 112 and/or control valve assembly 100 and, thus, external tubing 162 to vibrate, which can cause external tubing 162 to become dislodged or damaged, thereby affecting the operation of actuator 112 and, thus, the accuracy of the position of flow control member 178 relative to valve seat 180.
To address these problems, some known compact, multi-spring actuator apparatus can eliminate the need to employ external tubing to fluidly couple the controller and a chamber of the actuator by including internal passageways in the yoke, rather than external tubing. Control valve assemblies using compact actuators apparatus typically have the actuator spring(s) positioned within upper casing, rather than in yoke. With actuator spring(s) removed from yoke, yoke can be made smaller and an internal passageway can be drilled or machined longitudinally through body of yoke to fluidly couple controller to lower chamber of actuator. However, multi-spring actuator apparatus have the drawback that the pre-load of the springs are set by the size of the actuator casing and are not adjustable. Conversely, the pre-load of a single spring actuator can be adjusted or bench set.
As shown in FIG. 2, control valve assemblies 200 having compact, multi-spring actuator apparatus 210 typically have an actuator 212, a yoke 240 that is used to couple the actuator apparatus 210 to the fluid valve 270, and a controller 260. Similar to the actuator 112 shown in FIG. 1, actuator 212 has an upper casing 216, having a vent assembly 218, and a lower casing 220 secured to upper casing 216 with nuts 222 and bolts 224 and defining a cavity 214. A diaphragm 230 is secured at its edge between upper casing 216 and lower casing 220 and at an inner portion is positioned adjacent an upper diaphragm plate 236. Diaphragm 230 is positioned in cavity 214 to define an upper chamber 232 and a lower chamber 234. Unlike the actuator 112 shown in FIG. 1, actuator 212 also has one or more actuator springs 251 positioned within upper chamber 232, between upper casing 216 and upper diaphragm plate 236, to bias diaphragm 230, and actuator stem 246 toward fluid valve 270.
Yoke 240 has a body 242, which is smaller than the body 142 of yoke 140 in FIG. 1, which is secured to actuator 212 at a first end of body 242 and to fluid valve 270 at a second end of body 242, opposite the first end. Due to the smaller size of body 242, an internal passageway 256 can be machined, drilled, or otherwise formed longitudinally through body 242 of yoke 240 from the first end to an area proximate travel indicator 252. Internal passageway 256 is in fluid communication with lower chamber 234 and can be used to provide a control fluid (e.g., pneumatic air) from controller 260 to lower chamber 234 of actuator 212. An actuator stem 246 extends through body 242 and is operatively connected to diaphragm 230 through upper diaphragm plate 236, via a cap screw 264. A travel indicator 252 is mounted to body 242, near an end of actuator stem 246, and can be used to visually determine the position of flow control member 278 in fluid valve 270.
Controller 260 provides a control fluid (e.g., pneumatic air) to lower chamber 234 via internal passageway 256 in yoke 240 and can be mounted to yoke 240 to fluidly couple controller 260 and lower pressure chamber 234 of actuator 212.
Fluid valve 270 generally has a housing 272 that defines a fluid flow path from an inlet 274 to an outlet 276. A valve seat 280 is disposed with the fluid flow path and a flow control member 278 can be moved into and out of sealing contact with valve seat 280 to control the flow of fluid through fluid valve 270. A valve stem 282 extends from flow control member 278, through housing 272, and connects to actuator stem 246 via stem connector assembly (not shown).
In operation, controller 260 provides a control fluid through internal passageway 256 in yoke 240 to lower chamber 234 of actuator 212 to provide a pressure differential across diaphragm 230. The pressure differential causes diaphragm 230 to move actuator stem 246, and thus valve stem 282, such that flow control member 278 moves in a rectilinear path relative to valve seat 280 to control fluid flow through fluid valve 270.
To fluidly couple controller 260 to lower chamber 234, controller 260 can be coupled or mounted to yoke 240 and internal passageway 256 formed in yoke 240 to fluidly couple an outlet port of controller 260 to lower chamber 234 of actuator 212. Eliminating external tubing in this manner significantly reduces or eliminates the possibility of damage to external tubing that may otherwise occur, thereby increasing the accuracy and reliability of actuator 212 and fluid valve 270.
However, due to the size and height of yoke 140 in single spring actuator apparatus 110, a longitudinal internal passageway cannot be formed through yoke 140 from the first end all the way to an area proximate the travel indicator 152. The actuator spring 150 in single spring actuator apparatus 110 is large in diameter, long, and located inside the yoke 140, while the controller 160 is located low on the yoke 140. Due to the extended length and small diameter that would be required of a longitudinal internal passageway in a single spring actuator apparatus 110, standard drilling or machining processes cannot be used. In addition, an insert could not be used to cast a longitudinal internal passageway into yoke 140 in the casting process. Again, due to the extended length and small diameter, any insert used would be weak and would either break during the manufacturing process or would not be able to be removed.